1. Field of the Invention
The present invention is generally related to pressure sensors and, more specifically, to a pressure sensor that is particularly adapted to be used in association with a component carrier such as a printed circuit board or a generally planar ceramic member.
2. Description of the Prior Art
Pressure sensors of many different types are well known to those skilled in the art. Some types of pressure sensors incorporate silicon components that are micromachined to form a diaphragm on which one or more piezoresistors can be disposed. When the diaphragm moves in response to changes in pressure imposed on it, the piezoresistors experience stress and a corresponding change in resistance. The piezoresistors can be disposed in an appropriate bridge circuit arrangement to respond to movement of the diaphragm and provide an analog signal that is representative of the pressure imposed thereon.
U.S. Pat. No. 4,895,026, which issued to Tada on Jan. 23, 1990, discloses a semiconductor pressure sensor that comprises first and second pressure sensing diaphragms which each have first and second pressure receiving surfaces. The diaphragms are supported in a common plane in the same orientation. Two pressure sensing diaphragms are connected to similar bridge circuits made of piezoelectric elements for generating electrical signals indicative of the fluid pressure acting on the pressure sensing diaphragms. A first fluid passage is connected to a first pressure source and is disposed in fluid communication with the first pressure receiving surface of the first diaphragm. Similarly, the second pressure receiving surface of the second diaphragm is connected in fluid communication with a second fluid passage. The two electrical signals are supplied to a differential amplifier where the two signals are subtracted from each other and an output signal proportional to the magnitude of the difference is provided.
U.S. Pat. No. 4,656,454, which issued to Rosenberger on Apr. 7, 1987, discloses a piezoresistive pressure transducer that uses elastomeric seals. The low cost pressure transducer utilizes premolded elastomeric seals and is particularly adapted for automatic assembly. The stress sensitive element of the transducer is in the form of a diaphragm of semiconductive material that has a thickened rim. The semiconductive material is held at its rim between a pair of premolded elastomeric seals in a thermoplastic housing. Electrical connections with external circuitry are made with strain relief jumpers that connect conductive regions on the pressure sensitive element outside the seals to conductors which pass through the housing wall.
U.S. Pat. No. 4,889,590, which issued to Tucker et al on Dec. 26, 1989, describes a piezoresistive pressure sensor element that is formed in the front face of a silicon wafer. A thin diaphragm is formed under the sensing element by anisotropically etching a cavity from the rear face of the wafer. The rear face rupture pressure of the silicon diaphragm is at least doubled by subjecting the anisotropically etched cavity to a mild isotropic etch. This substantially improves the cavity side overpressure rating of the finished pressure sensor without any significant change in the device sensitivity.
U.S. Pat. No. 4,876,893, which issued to Kato et al on Oct. 31, 1989, discloses a strain gage for a pressure sensor which is made of an amorphous alloy including Ni, Cr and Si. The alloy has a high crystallization point and its temperature coefficient of resistance is almost zero. The alloy is a nonmagnetic substance and the strain gage produced with it is not substantially affected by external electromagnetic noise.
U.S. Pat. No. 4,721,938, which issued to Stevenson on Jan. 26, 1988, describes a process for forming a silicon pressure transducer. The transducer is formed in a silicon layer which has been grown over a monocrystalline silicon substrate. A central portion of the substrate had been earlier coated with a silicon dioxide layer having a plurality of apertures under each of which had been formed a heavily doped etched resistant region. The substrate is etched to remove its central portion under the silicon dioxide and the heavily doped regions to leave a thick surrounding portion to provide support. Resistors are formed in the monocrystalline portions of the grown layer overlying the heavily doped regions.
U.S. Pat. No. 5,081,867 which issued to Yamada on Jan. 21, 1992, discloses a semiconductor sensor that comprises a sensor member on a support member. The sensor member has a base portion and a rim portion connected to each other by a beam portion. The base portion is fixed to the support member and the rim portion is held by the beam portion such that the rim portion is spaced apart from the base portion and the support portion. The beam portion is provided with a resistor to detect the changes of resistance values of the resistor due to mechanical stress caused at the beam portion.
U.S. patent application Ser. No. 07/826,206, which was filed on Jan. 24, 1992 by Maurer and assigned to the Assignee of the present application, discloses a pressure transducer that provides a significant advantage by using elastomeric members that are selectively conductive. A pressure transducer is disposed between a selectively conductive elastomeric device and another resilient sealing member with a compressive force provided by two housing members. The selectively conductive elastomeric member provides electrical communication between components of the silicon pressure transducer and other electrically conductive components of the pressure sensor. The cooperation between the pressure sensor, which comprises a silicon diaphragm member, and the selectively conductive elastomeric member significantly decreases the cost of manufacture of the pressure transducer and improves its reliability.
U.S. Pat. No. 3,968,466, which issued to Nakamura et al on Jul. 6, 1976, discloses a transducer that includes a semiconductor diaphragm of a predetermined conductivity having a strain sensitive region capable of being elastically deformed by means of the external pressure applied thereto. The pressure transducer also comprises a fixing region having a high degree of rigidity, central and peripheral strain sensitive elements disposed along the crystallographic directions thereof and exhibiting high sensitivity. The pressure transducer transmits the electrical signals detected by strain sensitive elements to electrodes by means of lead portions and, in turn, conducts the electrical signals through the lead wires to processing apparatus.
U.S. Pat. No. 3,899,766, which issued to Mermelstein on Aug. 12, 1975, describes a pressure transducer which includes a pressure fitting, a diaphragm, a strain gage comprising a bridge circuit and tabs with leads for the bridge circuit. It also comprises a termination board. All of these components are contained within a case member. One end of the case is swaged over a flange on the fitting in order to sealingly clamp the diaphragm between a shoulder in the case and the fitting flange. The bridge portion of the strain gage is adhesively secured to the diaphragm.
U.S. Pat. No. 3,505,634, which issued to Von Vick on Apr. 7, 1970, discloses a differential pressure transducer that is adapted for providing an electrical signal indicating the pressure difference between two fluid media. It includes a flexible diaphragm having strain gage elements on its surface within the different fluid media whose pressure difference is to be measured. Positioning of the strain gage elements at the periphery of the diaphragm surfaces provides minimal sensitivity to applied line pressures. Protection from the media is provided by a layer comprising inherit organic material.
U.S. Pat. No. 3,457,536, which issued to Dean et al on Jul. 22, 1969, describes a subminiature pressure transducer that comprises a diaphragm sensing surface with sensors positioned to measure stresses in the diaphragm induced by pressure. The diaphragm is biased by a reference pressure which is applied to a side opposite the test pressure in order to prevent stress reversal in the diaphragm structure.
In an article in the Dec. 4, 1972 issue of Electronics, authors Sias and Hare discuss pressure transducers and the attachment of pressure transducers to circuit boards in an article entitled "Integration Brings a Generation of Low-Cost Transducers." The article discusses pressure transducers which use an all silicon vacuum reference chamber with a Wheatstone bridge arrangement of diffused piezoresistors to measure pressures ranging between zero and one atmosphere.
Elastic connectors, described as the W series, are available from the Fujipoly Corporation for use with electronic circuits and connection between two conductors. These devices provide high accuracy rubber connectors with anisotropic electrical conduction properties by providing between three hundred and two thousand fine metal wires per cubic centimeter embedded in the thickness direction of the transparent silicone rubber sheet. The connectors are inserted between opposite electrodes to provide electrical communication therebetween. The fine metal wires can be gold plated to insure that low resistance requirements can be met along with the ability to withstand relatively high currents. Fujipoly also provides low resistance ZEBRA elastomeric connectors that are constructed of alternating parallel layers of electrically conductive and nonconductive silicon elastomer material. The electrically conductive layers are filled with silver metal particles. The low resistance device provides a redundant connection with a minimum of two conductive layers per contact pad. The connector is available with an insulating barrier or silicon supports. These devices are used for connecting electroluminescent and plasma type displays to printed circuit boards or for connecting hybrid circuits to printed circuit boards. The connectors are positioned between two aligned surfaces and are mechanically clamped together with a lid or other printed circuit board. The connectors may be free standing or positioned in a retainer depending on packaging profiles and design.
In the August 1987 issue of CONNECTION TECHNOLOGY, author Buchoff describes elastomeric connectors in an article titled "Guidelines for Designing Elastomeric Connectors into the System." Also, in the Dec. 7, 1989 edition of EDN, author Mosley describes elastomeric connectors in an article titled "Elastomeric Connectors/meet SMT requirements." Many other articles are available and known to those skilled in the art of electronic circuit design and packaging. The principles of using elastomeric connectors which are selectively conductive in one direction are well known and understood by those skilled in the art. The United States patents and magazine articles discussed above are hereby explicitly incorporated by reference in this application.
In many applications, it is necessary to provide additional circuitry for use in association with a pressure transducer. This circuitry are in addition to the limited components that can be provided directly on the silicon pressure sensor die itself. The additional circuitry can be related to the provision of electromagnetic interference (EMI) protection or the provision of additional capacitors, diodes, trimmable resistors or thermistors which cannot be provided within the structure of the pressure transducer itself. Although silicon pressure transducers typically incorporate amplifier circuitry, piezoresistive components and some trimmable resistors and thermistors on the silicon die with the diaphragm, it is often necessary to provide additional component carriers, such as a printed circuit board, when capacitors and other larger components are necessary for use with the pressure transducer circuit. When this type of combination is necessary, it is common to attach a pressure transducer to a printed circuit board and connect leads from the transducer to components on the circuit board, either by extending leads between the two devices or by soldering leads of the pressure transducer to components or conductors on the printed circuit board. Significant damage can occur during this process because of the need to supply heat to delicate components to accomplish the soldering operation. The potential for damage during the manufacture of this type of device significantly decreases the yield of the finished product. In addition, when soldering is used to make electrical connects between components of this type, later failures can occur during operation if the procedure is not performed with near perfection.
It would therefore be helpful to the field of pressure measurement if a pressure transducer can be efficiently and reliably attached to a component carrier, such as a printed circuit board or a ceramic planar member, without the need for soldering or lead wire connections.